Tuesday, September 2, 2008

9.5 You are left-eyed?

No one can spin a better yarn about the eyes as the ancient Egyptians. In the Egyptian mythology, the right eye, aka the Eye of Re (or Ra), symbolizes the Sun. And the left eye, aka the Eye of Horus, is the Moon.

The Eye of Re has a mind of its own and frequently wanders around by itself. On one of the fun-filled outings, it refuses to return, so Re (the father of all gods) sends Shu and Tefnut, two underlings, to retrieve it. The eye stubbornly refuses. And in the ensuing struggle, the eye sheds tears and from which, men emerge.

Another story has it differently, Re actually sends Thoth to fetch it back. And upon returning, the eye discovers that it has been replaced by another eye and becomes quite indignant. To pacify it, Re places the right eye in the shape of the uraeus serpent on his own brow - to show that the eye is now the ruler of the world. This serpent is worn by all Egyptian Pharaohs on their headgears. The right eye later becomes an entity and its association with many goddesses is of course the basis of many other stories.

The story of the left eye, the Moon, is even more complex.

The lunar cycle actually represents the eternal battle between Horus and Seth. They are fighting for the inheritance of Horus's father, Osiris. Seth steals the eye and damages it - cuts it up into six pieces. Thoth, with the help of other gods, puts the eye back together on the 6th lunar day. The healed eye is known as Wadjet. It symbolizes a re-established order after disturbances. The lunar cycle is essentially a description of how the eye is injured and repaired. The latter performed by 14 gods.

For the mere mortals such as you and I, the two eyes also behave somewhat differently - in the form of ocular dominance. About 2/3 of the population sight with the right eye. Ocular dominance seems to correlate with the handedness, i.e., a right-handed person sights with the right eye. However, there are always exceptions; you can be right-handed but sight with the left eye and so on. The reason is simple, each retina is controlled by both hemispheres of the brain, whereas each limb by only one side.

Ocular dominance is actually quite interesting and practical at the same time. It is often why a patient notices a change in vision (i.e., when the dominant eye is seeing less well than the fellow eye) and seeks help. In monovision contact lens fitting, the first attempt is always to fit the dominant eye for distant vision and the fellow eye for reading. Sometimes, this does not work out and the patient actually does better with the dominant eye for reading. In monovision laser vision correction, the dominant eye is also selected for distant vision. You are of course stuck if this arrangement does not work.

Being very capable archers, the ancient Egyptians must have queried their eye doctors why some sighted with one eye vs the other. The mythology of the eyes, on the other hand, is a true testament to their vivid imagination.

Evidence of eye surgery in ancient Egypt? See the lower eyelid of the right eye in this mummy portrait:

10 comments:

Interesting mythology and interesting pictures!The mixture of mythology and eye science probably is very unique in academic articles, right?I am lucky that I don't need to wear bifocal glasses probably because of the dominant eye phenomena. Nice to know. Thanks!

That is indeed very lucky. If one eye is emmetropic and the other with a -2.50D myopia or less, and neither is caused by any pathology, then no bifocals are needed ever. Of course there is a slight trade-off in stereopsis. Airline pilots cannot have monovision, for example.

I'm right-handed, but left eyed.I only found this when I was in the army.For those who don't know how to check this, it's quite simple.Stretch your arms and forming a hole with your hands, point to an object with both eyes openned.The close one of the eyes and check if you're still seeing the object.If yes, then that's your dominant eye, if not, then it's the other.In my case, it's my left eye that keeps seing the object.

Very good. Indeed, that's one of the best ways of determining ocular dominance.

The dominant eye seems to see the same object as being larger than the other eye. This may explain why long-range shooting (e.g., at 300 yards or longer) is best done sighting with the dominant eye. For a left-eyed, right-handed person, it may be necessary to use a left-handed rifle, for example.

In the parochial schools in the old days, the Catholic nuns would force left-handed pupils to use their right hands - or risk punishment. Good thing they did not know some were left-eyed or we'd have seen many kids with the left-eyes patched.

Interesting point. Eye dominance is probably not associated directly with the handedness. It only appears to because more people are both right-handed and right-eyed. On the other hand, if both parents are left-eyed, or one R one L, the offspring are more likely to be left-eyed. Rarely are they left-eyed if both parents are right-eyed. Simply put, yes, there is a genetic factor in ocular dominance.